I think what Rudi wanted to say originally with "less noise" was to have a better PSRR. So, given that You are in the fiddling mood, maybe it could be tried as well to fit in, instead of the resistor feed, an another CCS.. Because of the higher dissipation, You could do it with an LM317 as a first approach, or a more elaborated LED-BJT CCS?
[On top of the zeners, to be clear]
It's just an idea, and I am not even sure, because Mauro has good points about the simple Zener shunt.
Maybe you even have tried it already? At least it would clarify if Rudi had some valid point in the better PS separation?

Increasing the supply voltage of the LM318 also increases its slew rate. I was reading the datasheet to see what sane values would be and decided to perform some experiments.

I actually like the shunt regulators better than the LM78xx/LM79xx as they are actually more quiet(noise wise, if you use a good quiet resistor) and let less AC ripple through to the LM318 (check it with a scope, if you have good zeners you will see there is less ripple).

So what I did, was I took two 18V zeners and popped em in, and then biased the LM318 class A with 7ma with an adjustable current source. I also tried a resistor for kick(3.3K as suggested) but the current source is better.

All I have to say is wow.

This amp has always been excellent, but now I think I am in heaven.

This is on my REV C monoblocs with no other mods at all.

Now keep in mind I have a 300Va toroid on each channel, so my supplies are stiff and clean.

Cheers!
Russ

Russ,
I have biased an opamp before using a pair of 2SK170's and a reisistor. How did you impliment it?
Going to the 18 volt zeners sounds like it should be my ticket also. Less heat off the 1K resistors to boot.

Russ,
I have biased an opamp before using a pair of 2SK170's and a reisistor. How did you impliment it?
Going to the 18 volt zeners sounds like it should be my ticket also. Less heat off the 1K resistors to boot.

George

Hi George,

I used LM334, but there may be even better constant current sources, but i have had exceelent results with those.

Good to hear that the Rev C gets better by the day (or is that by the hour?)

Some other mods that are worth considering include:

1. Discrete diodes, hi-speed, soft recovery of course. These normally result in a lower noise floor when replacing diode bridges

2. 100R in series with 330nF caps as snubbers across the diodes. Same effect as 1.

3. Double regulation for the 318's power supplies? This requires more work, but could be worthwhile based on experiences with NAIM pre-amps

4. Speaking of NAIM, I have always had excellent results from using oversized toroids to provide power supply. I know that Rudi is using relatively small transformers (20VA I think) and it would be easy enough to determine if using say a 100VA makes a worthwhile difference. I would expect it to result in further big improvements in bass resolution.

5. Now that the power supply voltage is at a decent level, it may be worth trying the 318 replacements (627, etc) again, as perhaps these made no difference in the past vs 318 because they were not receiving sufficient juice....

Thats about it from me for now. Anyone else with some ideas on pushing the boundaries?